play musical notes, how?

I'm trying to find out how to play musical sounds by specifying the pitch and other qualities. This seems to be what a guitar app or keyboard app does, but what part of the sdk is being used? I see ways of playing an ogg or mp3, but this isn't what is needed for musical app.

I'm not entirely sure, but on apps such as the piano, it seems easy enough that they probably just got the sound the first key makes, and onClick, just plays that sound, so for a custom one, I'm not entirely sure what you'd have to do, sorry. The only thing i can think of is doing just that, record the sound you want for each button. This is hard to help with if we're not sure what you're doing exactly